New crack found in toilet, way back (4,3)
I believe the answer is:
long ago
'way back' is the definition.
(thesaurus)
'new crack found in toilet' is the wordplay.
'new' becomes 'n'.
'crack' becomes 'gag' (I've seen this in other clues).
'found in' means one lot of letters goes inside another.
'toilet' becomes 'loo' (loo is a kind of toilet).
'n'+'gag'='ngag'
'ngag' going into 'loo' is 'LONG-AGO'.
(Other definitions for long ago that I've seen before include "Ages back" , "way back" , "In the distant past" , "Remote in time" , "Many years past" .)